A known capacitor insulated low-capacity power supply is configured to rectify and smooth an AC voltage applied to first and second capacitors, to use the rectified and smoothed voltage as power supply in a power saving mode of an image forming apparatus.
In the low-capacity power supply, the AC current flowing to the first capacitor and the second capacitors is originally minute. When the AC current fluctuates as the AC voltage does, the influence of the fluctuations of the AC current may influence over an operation of a smoothing circuit of the low-capacity power supply, so that a stable DC output might not be obtained.